Refractive Lens Exchange (Clear Lens Extraction) for Myopia Correction

Clear lens extraction (CLE), also called refractive lens exchange (RLE), is the removal of a noncataractous natural lens of the eye with or without intraocular lens placement as a refractive procedure.

This refractive procedure has been around for nearly a century, and, throughout that time, it has been in a sea of controversy. In the past 5-10 years, CLE has slowly become accepted as a viable alternative to other refractive procedures for selected patients.

CLE is usually reserved for patients with high myopia (>8 diopters [D]) that is not easily managed by other refractive procedures, such as laser in situ keratomileusis (LASIK) or photorefractive keratoplasty (PRK). However, CLE may be an even better choice for patients with high hyperopia (>4 D) than for patients with myopia because of the smaller risk of postoperative retinal detachment and the fewer modalities available to treat patients with high hyperopia.

Frequency

CLE still accounts for probably less than 1% of refractive procedures.

Myopia is believed to be a result of a genetic predisposition in combination with close work over an extended period.

Myopia is due to an axial length longer than the focal point of the refracting system of the eye or an overly powerful refracting system, a thick cornea, or a thick lens, or a combination of any or all of the above.

Myopia usually develops in early or mid teens and stabilizes in early adulthood. It presents as blurry distant vision.

Optical or refractive indications for lens surgery are ametropia (ie, myopia, hyperopia, astigmatism), anisometropia, and presbyopia. These include all classic refractive states of the healthy adult eye, which is why this new indication for lens surgery is controversial; no true histopathology may exist in most of these eyes.

Some eyes, as in those with extreme axial myopia, may be at risk for true pathology following surgical intervention. In addition, historical development of spectacles and contact lenses antedates the development of modern lens surgery. For these reasons, a mind-set has been created among academics that inborn errors of refraction are not diseases; therefore, they are not conditions to be treated by medicine or surgery, especially if such treatment might unnecessarily endanger an eye or expose an otherwise healthy eye to undue risk. This argument is rapidly losing credence.

The global anterior segment ophthalmic surgical community has embarked on a new and enticing endeavor called human emmetropia worldwide. The process began as an "idea before its time" in the 1950s, with the failed attempts at endothelial radial keratotomy of Barraquer and others at phakic anterior chamber intraocular lens (IOL) implantation.

The ophthalmic surgical technical revolution that ensued over the following decades allowed a return to the concept of the surgical correction of refractive errors 30 years later in the 1980s, this time as an "idea whose time had come." Refinements in ocular anesthesia, incision technology, lensectomy techniques, viscoelastic tissue protection, and IOL manufacture and implantation resulted in a return to the concept of intraocular correction of refractive errors, which includes both clear lensectomy and phakic implantation ^[1] . All this, combined with the seeming multitude of new keratorefractive procedures, led to the development of a new bona fide ophthalmic surgical subspecialty, controversial as it may appear, called refractive surgery.

The basic needs of refractive surgery are accuracy, stability, safety, and quality of vision.

Regarding accuracy, ideally, a standard deviation of less than 0.25 D is wanted, yielding 20/25 (or better) uncorrected acuity in 95% of patients for all amounts of myopia, hyperopia, and astigmatism. Currently, no procedure produces this result, but the closest are still LASIK or PRK for patients with low or moderate myopia and LASIK for patients with mild hyperopia. Currently, A-scan measurements and IOL choice, even using the IOL Master, especially in patients with high hyperopia and those with myopia, yield an accuracy of significantly less than ± 0.25 D.

For stability, CLE is probably the most stable refractive procedure available, with ± 0.02 D per year reported over a 9-year observation period. PRK has a significantly higher risk of regression or progression, and, in addition, LASIK carries a risk of corneal ectasia.

Several studies have shown that, for quality of vision, an unoperated cornea is optically superior to an operated cornea. Any operation on the cornea creates abnormal contours, which, in turn, create optical aberrations. The greater the correction, the greater the amount of induced aberration and the concurrent decrease in quality of vision, especially in low-contrast situations (eg, driving at night). Clearly, CLE is an optically superior choice in some situations.

Safety is discussed more extensively below.

Without question, the consequences of some complications (eg, endophthalmitis, retinal detachment) of intraocular surgery are much graver than the worst complications (eg, flap loss, corneal scarring requiring corneal transplant) of other refractive procedures.

Almost all operable tissues and spaces of the eye, including the corneal surface, the corneal stroma, the anterior chamber, the pupil, the posterior chamber, the lens, and the sclera, have been investigated as locations for refractive surgical modulation. Therefore, among others, the lens assumes its role as a popular location for surgical refractive modulation for those who prefer a familiar procedure that not only spares the cornea but also saves the economic expense of an excimer. Those who decry the lenticular approach emphasize all potential intraoperative and postoperative complications attendant with invasive intraocular procedures.

Despite the controversy, clear lens replacement is a viable procedure for both myopia and hyperopia, and toric IOLs are now available for intraocular correction of astigmatism. Multifocal IOLs and accommodative IOLs are now being used by many surgeons for the intraocular correction of presbyopia. Other attempts at development of a truly accommodative pseudophakos include intracapsular injection of liquid silicone, intracapsular placement of high-water content poly-HEMA lenses, liquid silicone-filled intracapsular balloon, multiple IOL implantation, polypseudophakia, and intracapsular placement of a flexible, plate-haptic, foldable, accommodative IOL.

Once thought of as an "idea before its time," surgical restoration of accommodation is becoming more of a reality. In 2003, the US Food and Drug Administration (FDA) approved the intracapsular placement of a flexible, plate-haptic, foldable, accommodative IOL, called Crystalens, for patients with cataracts. Crystalens was the first IOL to allow patients to focus on objects both at near and at distance without the use of spectacles or contact lenses. Working much like the natural lens of the eye, Crystalens, with its hinged haptics, facilitates back and forth movement along the optical axis of the eye in response to pressure changes that result from ciliary muscle relaxation and contraction. Since that early Crystalens, newer and improved versions have come out, and competitive brands with different modalities, such as ReSTOR ^[2] and ReZoom, have also entered the marketplace.

The surgical reversal of presbyopia is refractive surgery's "final frontier." Clinicians are exploring different techniques to surgically treat/reverse presbyopia (see Surgical Reversal of Presbyopia: A Comprehensive Video Text).

Indications for CLE are currently seen as the following:

• Myopia when other refractive procedures are contraindicated

• Myopia when other refractive procedures would give an inadequate result

• Hyperopia when other refractive procedures are contraindicated

• Hyperopia when other refractive procedures would give an inadequate result

CLE is performed as any other cataract procedure; the only difference is the decreased use or absence of phacoemulsification power and the almost exclusive use of aspiration. ^[3]

Ideally, this procedure is performed using a clear cornea approach, making a 3-mm or smaller corneal incision, creating a regular capsulorrhexis, performing aspiration within the bag, and placing an IOL of choice in the bag.

Contraindications include retinal disease. With high myopia, a higher rate of retinal detachment exists than with other types of refractive errors.

The prognosis is excellent.